The present invention relates to enhanced efficacy antiperspirant compositions containing strontium. It also relates to enhanced efficacy antiperspirant salts containing strontium and an amino acid or a hydroxy acid and particularly to stabilized aqueous solutions of such salts. The present invention additionally embraces methods of making these antiperspirant salts and solutions and compositions containing same.
Enhanced efficacy aluminum and aluminum-zirconium antiperspirant salts are well known and are described, for example, in GB 2,048,229 and U.S. Pat. No. 4,775,528. These salts are generally made by heat treating a relatively dilute solution of the salt (e.g., about 10% by weight) to increase its HPLC peak 4 to peak 3 ratio, then spray drying to a powder. These salts typically have an HPLC peak 4 to peak 3 area ratio of 0.7 or higher, with at least 70% of the aluminum contained in said peaks. However, these enhanced salts are also known to rapidly revert back to their non-enhanced state (for example, as evidenced by an HPLC peak 4 to peak 3 area ratio of 0.3 or less) in aqueous solution, particularly at concentrations greater than 20%. Consequently, the enhanced antiperspirant salts are generally only available in powder form and, thus, are generally only formulated into finished formulations as suspended powders in order to retain their enhanced efficacy.
In U.S. Pat. No. 6,042,816, there are described enhanced efficacy antiperspirant salts that are stable in aqueous solution. These salts include a soluble calcium salt such as calcium chloride and a soluble amino acid such as glycine. Typically, these salts have a Ca:Al+Zr weight ratio of about 1:1 to about 1:28 and an amino acid:Al+Zr weight ratio of about 2:1 to about 1:20. Because these salts retain their enhanced efficacy in aqueous solution, they have an advantage over conventional enhanced efficacy salts that revert to the non-enhanced form in aqueous solution.
In U.S. Pat. No. 5,804,203, there are described topical compositions that contain an irritant ingredient (e.g., organic alcohol, carboxylic acid, keto acid, peroxide, etc.), an anti-irritant divalent strontium cation, and a cosmetic or therapeutic active ingredient. The strontium cation is said to reduce skin irritation that would otherwise result from the irritant ingredient. Example 11 illustrates an antiperspirant composition that includes aluminum chlorohydrate, ethanol and strontium nitrate. This composition does not include an amino acid or a zirconium salt.
In U.S. Pat. No. 5,788,956, it is suggested that perspiration can be controlled by topically applying a substance P antagonist. Various substance P antagonists are disclosed including peptide and non-peptide nitrogenous derivatives and salts of monovalent, divalent and trivalent cations. The latter includes strontium, magnesium, cobalt, nickel, manganese, barium, etc. Examples 1, 3 and 4 of the patent disclose compositions containing strontium chloride or strontium nitrate. However, the patent does not provide any sweat reduction data for the exemplified compositions. In contrast to the suggestion in this patent, it has been found that a clear gel product containing 5% strontium nitrate does not provide any measurable sweat reduction.
It would be highly desirable to provide enhanced efficacy antiperspirant compositions with superior efficacy, and particularly to provide enhanced efficacy antiperspirant salts which are stable in aqueous solution. This would make it possible to use the enhanced salts in finished formulations that require a soluble salt form, such as the currently attractive clear gel compositions that have been successfully introduced in recent years. It would also be highly desirable to provide a method of making enhanced efficacy antiperspirant salts in concentrated solution—i.e., at salt concentrations greater than 20%. Such a method would be more efficient than current methods, which generally require dilute solutions, thus necessitating removal of large amounts water to obtain the powdered salts.